Deprecate link-mtu

This options might have been useful in the past but nowadays it has a very
unclear semantics, so better remove/deprecate it.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20220101162532.2251835-2-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg23496.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/doc/man-sections/link-options.rst b/doc/man-sections/link-options.rst
index 32e72a1b7a14e2e63968b53022fb49674fd20257..b1ae4e75abc2ac674f0fcffcf5f5d2ba4d88ccd6 100644 (file)
--- a/doc/man-sections/link-options.rst
+++ b/doc/man-sections/link-options.rst
@@ -82,10 +82,15 @@ the local and the remote host.
          ping-restart 60            # Argument: timeout
 
 --link-mtu n
-  Sets an upper bound on the size of UDP packets which are sent between
+  **DEPRECATED** Sets an upper bound on the size of UDP packets which are sent between
   OpenVPN peers. *It's best not to set this parameter unless you know what
   you're doing.*
 
+  Due to variable header size of IP header (20 bytes for IPv4 and 40 bytes
+  for IPv6) and dynamically negotiated data channel cipher, this option
+  is not reliable. It is recommended to set tun-mtu with enough headroom
+  instead.
+
 --local host
   Local host name or IP address for bind. If specified, OpenVPN will bind
   to this address only. If unspecified, OpenVPN will bind to all

diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 7d48d6f2a548561ca0bbcd886a27571877f78ceb..32ba34aa9f6fb728cbcd505535fcddf427e96501 100644 (file)
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -2112,9 +2112,7 @@ options_postprocess_verify_ce(const struct options *options,
      */
     if (options->ce.tun_mtu_defined && options->ce.link_mtu_defined)
     {
-        msg(M_USAGE,
-            "only one of --tun-mtu or --link-mtu may be defined (note that "
-            "--ifconfig implies --link-mtu %d)", LINK_MTU_DEFAULT);
+        msg(M_USAGE, "only one of --tun-mtu or --link-mtu may be defined");
     }
 
     if (!proto_is_udp(ce->proto) && options->mtu_test)